System for preventing overheating of x-ray tubes and the like



Jan. 2, 1951 w. v. OFFUTT 2,536,306

SYSTEM FOR PREVENTING OVERHEATING 0F X-RAY TUBES AND THE LIKE Filed May 1a, 1946 INVENTOR. W. 1 Offui i ATTORNEYS Patented jan. 2, 1951 UNITED STATES PATENT OFFICE SYSTEM FOR PREVENTING OVERHEATING OF X-RAY TUBES AND THE LIKE William V. Offutt, San Marino, Calif.

Application May 13, 1946, Serial N 0. 669,442

13 Claims. 1

This invention relates to overheat control systems for electrical devices and more particularly to a system for preventing overheating of X-ray tubes.

It is an object of my invention to provide a system usable in conjunction with any electric current consuming apparatus for the purpose of interrupting current in the apparatus circuit in response to a predetermined heating effect in a portion of the system constituting my invention, whereby undue heating of the apparatus is prevented.

It is another object of my invention to provide a system to be used in conjunction with a conventional X-ray tube for the purpose of interrupting current to said tube to prevent the tube from becoming unduly overheated.

It is a further object of my invention to provide an electrical system for interrupting current to an X-ray tube in response to functioning of an element so devised as to close contacts at a predetermined point corresponding to a predetermined temperature of an X-ray tube.

It is a, still further object of my invention to provide my system with a thermal element so devised as to simulate the heating characteristic of any particular X-ray tube and operative to cut off current to that tube at a predetermined point prior to heating of the tube to a detrimental degree.

embraces a thermal element having a plurality of resistances adapted to be connected to an X-ray transformer so that the voltage across the primary and the current flowing in the secondary are commuted into heat energy causing expansion of air in a chamber housing the resistances.

The air thus expanded compels motion of a mercury globule or pellet in a capillary tube connected to the housing but against the reaction of an air pressure dome, the combination being mechanically and electrically arranged so that motion of the mercury globule is operative to electrically bridge a pair of spaced contacts disposed within the capillary under conditions predetermined by design to cut off power to the transformer prior to overheating of the X-ray tube. Incorporated in the system are various elements operative to re-energize the transformer after due period of cooling has been allowed, such re-energization taking place automatically in response to cooling and contraction of the previously expanded air as heat is dissipated from the thermal element, all as hereinafter described.

My invention is illustrated in the accompanydrawing which shows an X-ray transformer Tl in conjunction with an auto transformer A which is manually controllable to determine the strength of the rays in a well known manner. A solenoid operated switch Swl, a push button or timer unit, Sw2, and on-oii switch, S103 are connected to the transformers as shown. The elements thus described are conventional, commercially obtainable devices and are generally provided as part of a complete X-ray outfit.

My invention utilizes in addition to the aforementioned elements, a thermal element H, together with ballast resistors RI, R2, and a voltage transformer T2, as well as a pair of relays S2 and S3.

The element H comprises a comparatively large, thick-walled glass enclosure ii) in which is secured in any suitable manner a pair of resistances R3 and R4. Adjoining the chamber In and in communication therewith is a capillary tube 14 having spaced metallic sleeves H, is and 2! fixedly secured and sealed therein and which tube I4 communicates with a pressure reactance dome 25. A globule or pellet 39' of mercury is provided in the lumen of the tube and is adapted to flow easily in either direction through the sleeves, being proportioned in quantity so as to be capable of extending between the sleeves i'l- H! or l92l to provide an electrical contact therebetween under certain conditions to be hereinafter described. The resistances RI and R2 are provided for the purpose of matching the resistances R3. and R4 to the secondary and primary, respectively, of the transformer Ti so as to convert the secondary current and primary voltage into heat energy in proper proportion to reflect the heating characteristic of the X-ray tube. The transformer T2 functions to increase the current in resistance Rt whereby to slightly raise the temperature of that resistance in order to assist in the proportioning effect. The dome 25 is of such dimensions as to provide a proper pressure reaction to the mercury pellet 30 when it is forced to the right by heat expanded air in chamber l6 so as to ensure the ultimate result, i. e., close simulation of the heat characteristic of any particular X-ray tube in terms of motion of the mercury pellet. It will be understood that the various values for the resistances R! and Rd, transformer T2, and the size of dome 25 may be suitably proportioned as a matter or" design to achieve the effect of causing motion of the mercury pellet 3D to a predetermined extent for bridging contacts at l'l-l9 or l92l in accordance with certain conditions as will be hereinafter described In general, resistance R3 should have as highervalue than resistance R4 since it is connected in the secondary of the transformer Tl (at ground potential point), the milliammeter leads provided on the secondary of conventional transformers being suitable for connecting R3 in series with the secondary coil. The 1. ratio values between R3 and a4; is. dependent inter alia upon the ratio of voltages across the primary and secondary and should be of" such value as to jointly produce a temperature inthe chamber iii fluctuating in accordance with voltage and current variations-in the transformer primary and secondar Soasto reflect proportionally the resultant variations in, temperature of the X-ray tube used: in. conjunction with the system.

The relay S2. comprises. a. nor-mally closed contact arrangement 35} andnormally opened contact arrangements 3'! and 6! while the relay S3 has the single normally closedcontact arrangement 43. It will be understoodthat. the reference characters 35 tl1rough-fi3Jrefer in eachcase to a pair of contacts each of which consists of an armature anda fixed-point as symbolized on the drawing.

Inthe present instanceitis assumed that. the P system is fed by a 220 volt line, as indicated by the conductor legs aand b,which 220 volts may be fully applied across primary transformer Tl but is generally-reduced in value by manipulation of a knob K of the auto-transformer A in amanner and for a purpose well understood by persons skilled in the art. As will be apparent, contact arrangement as of switch Swi is normally closed when circuit continuity-provided at $1.02 and S103, there being a potential of 110 volts provided, by transformer A to energizeSwl under th conditions shown on the drawing. The energizingcurrent fromthe transformepAv istapped oifthrough legs 0, and-d which are indicated as plus and minuarespectiyely, to indicate polarity at an assumed instant. Accordingly, with push buttonSwZ and switch-S1113 closed, a current flows through' sw l energizing it such current following a course throughvarious-conductors legs (assuming the current to flow from positive to negative) .of ce,Swlf-contact 35'gd; At this time relays S2 and s 3 are not energizedand the complete systemmay be assumed to be operating normally, no undue heating o f the X-ray tube taking place.

In the event that thevoltage across the primary and current in the. secondary of transformer Tl becomesuch duetoincreasein line volt ge, etc, that the X-ray tube wouldbecome unduly heated prpporfional currents flowing in-resistances R3 and Rd, cause a heating: oflthe; air in chamber ill. Accordingly, expansion of. air in chamber it forcesthe mercury pellet 3fi irom its normal. position, as S11 0Wn, 't0Wald the right through sleeve. l'lv anr i along the lumen; of; the capillarytube 5 4 Although the mercuryprovides a bridge across the sleeves i;";.! S- at thisjime no fie s -p c uc di h eby;ow n e h -n rm y pen whea -z 4! ii avv .2;. Howev r cn in d h i n hamberl m t l causes the mercury pellet to bridge the gap between sleeves i92 I. When this occurs the relay S2 is energized, the circuit thus formed consist ing of conductor legs chj-mercury 3fi sleeve 2lk-Zthe solenoid of S2-m n Sw3d. Energization of S2 in this manner causes interruption of contact 35 breaking the circuit heretofore described through solenoid Swl and interrupting, byrvirtue oi opening; of contact at as, the current tothe primary of transformer Tl. Energization of S2 also serves to cause contact engagement at 37 which sets up a holding circuit via the conductor, legs ch-p contact 31- contact 43 Z..solenoid of S2-mn-Sw3d, whereby S2 is maintained energized. As long as the temperature inchamber ill is such as to maintain the mercury. pellet 3E! in abridgement across sleeves 5 92*! against the reaction oi the air which has been compressed in dome 25 by the piston like effect of the travel of the mercury pellet in passing from the. normal position. to the abridging position; reay 52. il emain; n gi ed; n sc nc d tch Sw i Will beiniopenconditiomat. 4.9,.- l-Zoweyer, a further effect of the energization of relay 8,2;is

to close. contact atj thereby; connecting sleeve II. to the negative side. of the 11!); voltsource through thesolenoidof, S3. Accordinglyywhen the empe atu e d pssh atis issipated m chamber iii,- and. it. will be; undierstood that the chamber. is. so designed, as to ,dissip a te heat-.at substantially. the. same; rate as, the Xfray, tube. in conjunction with which it is used, the reaction pressurev in dome 25 .f orces mercury, pellet. 30; to move to=the leftagainst the decreasing pressure in. chamber Ill. Ultimately; the. mercury pellet bridges the contact l7..l 9. therbyclosing a; circuit comprising. the solenoid of relay fiiisto enersi e h relay, 'Ifhe circuitbthus. set, uplconsists of, conductor. legs. c- -h .jqsleeve; lS-. mercury 3l] .sleeve. liwr-econtact dl-etrsolenoidi S37 uTn--Sw,3,,+d. Accordingly,energization of re;- layv S3. breaks the, contact. engagement at... 43 thereby aking theh ine i cuit ftr layzsl whereby relay S2- is. de-energized; and: normal conditions, asshowrn on; thedrawing; are;r e#

stored.

It will now-beepprsciated; that I have disclosed a sys m to e me a on unc ionlw thconventional X- ay; ipmen or. -pmtec ine; -X: ay tube from overheating and which system Sim;- ple, effective and easily; installed, However, I believethat the essential teachi g ofgny invention is ot im tedl o se th Xr fi p aratus b ay, infact, ln s tahle:mo ufi at e i nd t i n irc i ere; o er t n Qt: an

l m n res n sanrpblem-e han it i lbev liyim i 'l i ensskillesil n h mitt-t t va ei liansesia a sl sclosnremar emader l w he ev r l ments i-. .iy inv nnor" x l e: h rmal; l ment is liu tr dw s tiliz nsai apnhrnube @I -iwhereby a: rge mev ent; o he; merc ry pell t; 39: is iiected; r; m ll. han s; n: ir: PFB$IIITQ2 in hamb r; fi;.wh c z c nfirm tion w properly re ertic i d1- mett nstitutesa.v. ysensitive devi e owells-n. it: will: be. pp ecia ed; hat fiaidsfith hanain duld.ha t li dretg-i eases i s of: uitable: xpansion-i chara eristics.- he. s sitivi y; f the; devi e is; dependent n ra a-l nr h volume; of; chamber; so; andithe e ative voiu' ae0.id@m r 5 .ivh 11;, v lume are usiectz dde iensui e ea ar eci. .z stal ations. heae ti ularrprpper iceineshownl zn he draw-.- riess i iser nu elrll trative u oses;

QQ H i lY; i Q1l93 n QQ '1 9:b heundabv he specific illustration hereinabove described except as set forth in the appended claims.

Having thus described my invention, I claim:

1. A system for protecting current consuming devices such as X-ray tubes and the like from overheating, comprising a thermal element for commuting current energy to heat energy and having a series of spaced contacts serially arranged and movable conductor means responsive to changes in volume of a thermoexpansive gas and positioned thereby for successively bridging pairs of said contacts in the series and rendering them electrically conductive in response to a predetermined degree of heat energy commuted within said element, and relay means adapted to be energized when a first pair of said spaced contacts are bridged to interrupt current to said current consuming device, said relay means comprising a first contact means adapted to be normally closed and through which current normally passes and adapted to be opened to break current passage when said relay means is energized, means whereby said current consuming device is energized during continuance of said current through said first contact means, said relay means also comprising a second contact means adapted to be normall open and adapted to be closed when said relay is energized, means whereby said relay means remains energized responsive to continuance of current through said second contact means, and said relay means having a third contact means arranged to be normally open and adapted to be closed upon energization of said relay means, and circuit means comprising a second pair of said spaced contacts and said third contact means for deenergizing said relay means on bridging of said last mentioned contacts in response to dissipation of heat energy from said thermal element.

2. In a device as set forth in claim 1 wherein said circuit means comprises an additional relay operative by said thermal element upon dissipation of heat therefrom to de-energize said first relay, said additional relay having contact means in series with said second contact means.

3. A system for protecting current consuming devices such as X-ray tubes and the like from overheating comprising, in combination, a current responsive el ment for commuting current enery into heat energy and adapted to be connected to a current consuming device in such a manner as to generate heat energy in proportional response to the current energy consumed by said current consuming device, said element having movable current conductor means responsive to changes in volume of a confined thermoexpansive gas and positioned thereby relative to three spaced contact members serially engageable by said movable means, said movable means being adapted to bridge a first and second contact member or said second and third contact member, in the order named and in reverse order, and means responsive to bridging of said second and third member for interrupting current to said current consuming device and restoring means responsive to bridging of said first and second members to restore current to said current consuming device.

4. In a device as set forth in claim 3, wherein said movable means has a normal nonbridging position adjacent said first contact member.

5. In a device as set forth in claim 3 wherein said means responsive to bridging of said second and third contact members comprises a relay energizable by current through said second and third contact members and said movable member, and having a normally closed contact means adapted to be interrupted upon energization of said relay, said current consuming device being adapted to be de-energized upon interruption of said contact means, said relay having a normally open contact means adapted to be closed upon energization of said relay and said restoring means comprising said last named contact means and said first contact member for de-energizing said relay when said movable element is in subsequent position bridging said first and second contact members.

6. In a device as set forth in claim 3, wherein said means responsive to bridging of said second and third contact members comprises a relay energizable by current through said second and third contact members and said movable member, and having a normally open contact means adapted to be closed upon energization of said relay, and a holding circuit including said contact means adapted to maintain said relay energized by current through said contact means.

7. In a device as set forth in claim 3 wherein said means responsive to bridging of said second and third contact members comprises a relay having a normally open contact means, said relay being adapted to be energized when said movable member bridges said second and third contact members, whereby said normally open contact means is closed, and said restoring means comprising said contact means and being operative in response to bridging of said first and second contact members to conduct current through said contact means to de-energize said relay.

8. In a device as set forth in claim 3 wherein said means responsive to bridging of said second and third contact members comprises a relay having a normally open contact means, said relay being adapted to be energized when said movable member bridges said second and third contact members whereby said normally open contact means is closed and said restoring means comprising said contact means and being operative in response to bridging of said first and second contact members to conduct current through said contact means to de-energize said relay, and wherein said restoring means comprises an additional relay, having normally closed contact means adapted to be opened upon energization of said additional relay, said additional relay being energizable only when said first-mentioned relay is energized upon abridgement of said first and second contact members by said movable member, including a holding circuit for said first-mentioned relay comprising said normally closed contact means of said additional relay whereby said first-mentioned relay is de-energized upon energization of said additional relay.

9. A system for protecting current consuming devices, such as X-ray tubes and the like, from overheating, comprising a power supply means including a transformer having a primary and a secondary, the secondary of which is adapted to be connected to an X-ray tube or the like, a safety current responsive device comprising a closed air chamber having a heater resistance therein connected in series with said secondary and responsive to the passage of electrical energy therein to heat and expand the air in said chamber, a tubular extension communicating with said chamber and having spaced contact means secured therein, a movable conductor element in said tube in normally non-bridging relation to said contact means but adapted to be moved by menace heated air. expanding fromsaidwehamberto bridge Said; contact; means; inz response tor a: predet e mined. degreepof expansionof air, in: said chameher, relay: means; adapted, to; be energized when. said; conductor element: bridges/a s-aidcontacts; relay; contact; means; being; operative to, control the; current to: said current; consuming; device; said; relay contact. means being adapted; to open anddnterrupt. current to' said; current. consuming devicew-hen, said. relay means is energizedl 10, A system for. protecting: currentconsum=- ing devices. asset .forth .in claim: 9. anda second. heater resistance in said chamber connected in. parallel; with the. primary-- of said: transformer, the; energization: of said-a secondary: heater resistance beingcontrolledby the operation of said relay means.

11; A1, system for; protecting; currentncons-umaing devices such. as X-raytubes-and the: like from overheating comprisingincombination, a current, responsive; element for. commuting cur rent energy into heat energy and adapted to, be connected to; a current consuming; device in such a manner as to generate heat energy in proportionalzresponseato; the currentaenergyrconsumed by, said. currentconsuming device; said elementhaving; means, movable byrgeneration .ofv heat, and-,threespaced contact members'serially engageabler'by said movablemeans; said movable means-beingadaptedto bridge. a'first. and second Contact. member or a; secondand; third: contactmember, in the order named and inreverse order, andimeans responsive to-br-idgingof. said second; and third member for interrupting cure rent toxsaidicurrent consuming device: and re.- storing. means responsiveto bridging of said first and-secondmembers torestore current to. said current consuming device said. contact members comprising sleeves secureda Within. a capillary tube,- and said movable. means compris inga mercury pellet in saidttube adaptedrtofiow. from a normal nonbridgingposition through; at least one-of saids1eevesto a bridging: positionz 12. A1 system for. protecting :current: consuming devices suehaasiXi-ray tubes. and t'hGJlikflfI'OIIl overheating comprising, .in combination, a; cure rent responsive element; for commuting current energy, into heat? energysand? adapted to be. con-.- nected to. a currentaconsuming: device in: such 1 a manner as: to. generate a heat energy in propor-'- tional response. to. the current. energyconsumed by; said; current consuming device; said element having, means: movable: by generation of. heat; and. three spaced contactimembers serially engageable: said movable means,-. said; movable means being adapteditoibridge arfirst andr'second contact. member" or asecond and: third, contact member,- in .theordennamed-and-in reverse order, and: mea ns;responsive.-to: bridging; of; said second and third; member;- for, interrupting current; to said current? consuming: device, and: restoring means; responsive: to. bridging of" said first; and second. members; torrestore: current: to. said: cur-+- rent, consuming device. said; contact members comprising. sleeves: secured; within: at. capillary tube-and saidmovable:meanepomprisinga mere cury; pellet: adapted: to: flow: in said. tube. from a normal nonbridging; position; through. said first contact: member to: a bridging; position. within the second contactzmember; thencev through.- said second contact member: to agbridging position with ,saidgthirdj contact member-.1

13.; A- system for protecting current: consumingdevicesssuch as Xeray tubes and. the likefrom overheating comprising, in combination; a. current responsive element: forcommuting. current energy; into heat energy andiadaptedi to: be con nected; to; a:= current consuming: device in such: a

v manner as-:to1- generate heat energy in. propertionalz, response: to... the :current' energy consumed byksaid: current I consuming. device, said elements having a series-.offspacedlcontacts" serially arranged and movable; gas pressure responsive means-1 positioned by changes; in volume of a thermoexpansive gas for. successively. bridging pairs of contacts in; the. series and means responsiveto; bridging: of one?pair. of' said contacts for interrupting, currentito said: current consuming; deviceand: restoring means. responsive to bridging: of. another: pair of said: contacts to restore current.toqsaidzcurrenticonsuming device;

V. OWUTT.

REFERENCES CITED The followingreferencesiare of recordzin the of'this. patent 1.

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